Jordan Thieme

I just finished up an LS swap in my 1984 Porsche 928S. I put in a 2008 LS3. I am struggling getting the speedometer and tachometer working. Here is what I have going on so far with them.

1. For the speedometer, I have an Intellitronix GPS sending unit the produces 4,000/8,000/16,000 pulses per mile. I hooked it up to the brown wire with the red stripe from the larger silver box under the center of the dash. When comparing this to my speed readout from my phone, it was off. The 8,000 one seems the closest with it reading about 60 on my phone and about 75 on the speedometer. Any idea what I am doing wrong? Maybe it does not have the correct pulse setting?
2. For the tach, I have the white wiring from my PSI wiring harness hooked up to the green wire show in the picture. It is not showing anything, which I assume is because I need a resistor inline with the wire. I have heard that a 4.7 kohm or 10 kohm will work. I am going to try and get both and test out, but wanted to make sure I had the right wires.

Thank you all for your help!

Speedometer wire removed from this connector.

Close up of Brown wire with red stripe I hooked the GPS pulse to.

Large green wire going into connector for tachometer.

Jordan Thieme

Any thoughts on the speedo? Maybe I need another one with a different pulse rate?

For the tach, I ran a 12 volt switched line to the white tach wire from my LS wiring harness and then ran both of those through a 4.7k Ohm resistor to the wire shown above. The tach did not move at all.

Any help is appreciated. I would prefer to use my stock gauges, but might have to just swap them all out over the winter.

icsamerica

Are you using a 0411 PCM? Do you have HP tuners?

With HP tuners you can use it to adjust the pulse rate. There is a wide range of adjustability and I was able to get a 0411 to operate and 80's Jaguar speedometer perfectly. I never LS swapped a 928 though so I'm not sure exactly how to do it but perhaps someone here knows the PPM and can post it. If you dont have HP Tuners then you'd have to do it the old way with a Dakota Digital SGI-100BT. I dont recomment this, there is no reason to add the complexity of another box when you're PCM can simply be programmed right.

Same goes for the tachometer. There is a setting in HP tuners to add the pull down resister in the PCM and also adjust the pulse rate.

Bulvot

The factory speed sensor sends 8 pulses per tire revolution. The stock tire size is about 25.1" in diameter, which works out to 803 revolutions per mile, or 6,428 impulses per mile.

The whole formula: Pulses per Mile = (feet per mile / ((tire diameter(inches) * Pi) / inches per foot)) * pulses per tire revolution

With numbers: Pulses per Mile = (5280 / ((25.1 * 3.141593) / 12)) * 8

The simplified formula: Pulses per mile = 161345 / Tire Diameter(inches)

Just plug in whatever your tire diameter is and you'll have the correct pulses per mile.

Jordan Thieme

I am sorry, I forgot to mention one very important part, I also swapped out the transmission for a 2001 Corvette Z06 6 speed manual.

Bulvot

Doesn't matter. You're trying to get the porsche factory speedometer to work. It is expecting 8 pulses per tire revolution.

Koenig-Specials 928

Why not attach the GPS Speed Sensor wire to the correct brown/red wire coming from the original sensor wire in the wheel well.
Throughout this car there are miles of brown/red wires. However, at the wheel well there are only 2 and the pulses are sent by the one with a bit of green paint on the first inch from the connector. If you try one and it doesn't work (no green paint) then it's the other. No other choices. Actual connection is made by the fuel tank level cover after tracing the line to a comfortable location to make the connection

I have a 2004 Z06 6 speed as well and that's where my Autometer GPS Speedometer Sensor is attached to.

Jordan Thieme

So I ended up getting the Dakota Digital SGI-100BT so I could tweak the speed pulses. I am pulling the speed signal directly from the LS computer and have it running pretty much dead on up to around 80 mph. After that, it lags behind actual speed. I have a Scangauge II hooked up to the computer and that is reading speed correctly, so I know the signal from the computer is accurate. Anyone had problems like this?